Accessory drive mechanism

ABSTRACT

An engine accessory drive mechanism wherein a first pulley portion is driven by the crankshaft and a second pulley portion is mounted on the water pump shaft and driven by a belt interconnecting the two pulleys. The second pulley portion includes provisions formed thereon for mounting additional belts to drive the other engine accessories. Each pulley portion includes one wall which is movable in response to changes in engine vacuum, with the influence of the engine vacuum on the movable walls being modified by the action of centrifugal force, the flyweight mechanism therefor being mounted on the first pulley portion, and the overall result being that the interconnecting belt is moved alternately in and out of the variable pulley grooves, changing the respective pitch diameters as required to drive all the accessories at a substantially constant speed throughout the full range of engine speeds.

I United States Patent 1151 3,653,283 Betz 1451 Apr. 4, 1972 54ACCESSORY DRIVE MECHANISM 3,269,207 8/1966 Borsattino ..74/864 [72]Inventor: David w. Ben, Dayton, Ohio 3,557,640 l/ 1971 Hendnks et al..74/230.17 F X [73] Assignee: General Motors Corporation, Detroit,Primary Examiner-Carlton Cmyle Mich. Assistant ExaminerThomas C. Perry Id J 8 1970 Attorney-Warren E. Finken, A. M. l-leiter and John P. Moran[21] Appl. No.: 44,155 ABSTRACT An engine accessory drive mechanismwherein a first pulley 52] U.S. c1 ..74/864, 74/23o.17 F, 74/230.17 MPmion is driven by the crankshaft and 3 9 Pulley pqnion 51 1 1111. C1..B60k 21/10, Fl6h 9/18 the Water P Shaft and dflven by a s 58 Field ofSearch 74/863, 864,230.17 E, 230.17 F, cmmectmg P F pulleys- The secondpully W 9 74/211017 M eludes provisions formed thereon for mountingadditional belts to drive the other engine accessories. Each pulley por-56] Reierences Cited tion includes one wall which is movable in responseto changes 1n engine vacuum, with the influence of the engine vacuum onUNITED STATES PATENTS the movable walls being modified by the action ofcentrifugal force, the flyweight mechanism therefor being mounted on the2,909,071 10/1959 Smyth et al ..74/230.17 E fi pulley portion and theoverall result being that the inter 2916924 12/1959 Dodge 230-17 Econnecting belt is moved alternately in and out of the variable2,260,798 lO/ 1941 Burns ..74/230.l7 F X pulley grooves, changing therespective pitch diameters as 2,521,457 9/1950 "74/230-17 E required todrive all the accessories at a substantially constant 5 333 23? i g 3, 1speed throughout the full range of engine speeds. 3:l57:066 1 H1964Donley et a1 ..74/230. 17 F x 5 Claims, 3 Drawing Figures I, ,v, i 1d?a. a 1 v PATENTEDAPR 4 |972 SHEET 1 [1F 2 Z d n5 A W ACCESSORY DRIVEMECHANISM This invention relates to accessory drives and moreparticularly to a belt drive for driving the accessories of a vehicleengine at a substantially constant speed irrespective of variations inengine speed.

In the operation of internal combustion engines in automotiveapplications, it is desirable that the accessories, such as coolingfans, generators, power steering pumps and air conditioning compressors,for example, be driven at a substantially constant speed for mostefficient operation of the accessory itself and also to reduce powerconsumption and noise by preventing the accessories from being driven atexcess speed.

Accordingly, an object of the invention is to provide an improvedaccessory drive unit for driving the accessories of a vehicle engine ata substantially constant speed.

Another object of the invention is to provide an improved accessorydrive mechanism wherein a first pulley assembly is driven by the enginecrankshaft, while a second pulley assembly is mounted on the water pumpshaft, including provisions for driving the cooling fan and the waterpump impeller directly, and the other accessories through a plurality ofbelts, in response to rotation of the second pulley assembly by aninterconnecting belt driven by the first pulley assembly; and includingmeans for varying the pitch diameters of both pulley assemblies, asrequired to drive the accessories within a predetermined relativelynarrow speed range.

A further object of the invention is to provide such an improvedaccessory drive mechanism wherein the means for varying the pulley pitchdiameters is responsive to engine vacuum, the effect of the latter beingmodified by the action of centrifugal force.

A still further object of the invention is to provide an improvedaccessory drive mechanism wherein one belt supporting wall of each oftwo pulley assemblies is axially movable in response to changes inengine manifold vacuum, with said walls being further influenced by theadmission of ambient air by valve means responsive to the action ofcentrifugal force representative of engine speed.

Still another object of the invention is to provide an engine accessorydrive mechanism wherein one pulley assembly is driven by the crankshaftand includes first and second housings whose adjacent walls serve as aV-groove for a belt, and a second pulley assembly is mounted on thewater pump housing and includes third and fourth housings whose adjacentwalls serve as a second V-groove for such belt, the first and thirdhousings including vacuum-responsive means for axially moving theirrespective walls of the two V-grooves, the second housing includingflyweights for varying the opening of a valve to admit ambient air intothe first housing and into a passage interconnecting the first andfourth housings, and the fourth housing having a plurality of groovesformed thereon for driving additional belts connected to various engineaccessories.

These and other objects and advantages will be apparent when referenceis made to the following description and accompanying drawings, wherein:

FIGS. 1 and la are cross-sectional views of an accessory drive systemembodying the invention; and

H6. 2 is a table of operating characteristics.

Referring now to the drawings in greater detail, FIGS. 1 and laillustrate an accessory drive system having a lower pulley portion 12which is mounted for rotation on an engine crankshaft 14 extending froma conventional engine 15, and an upper pulley portion 16 mounted forrotation on a water pump shaft 18 extending from the pump impeller 19 ofa water pump 20. The lower pulley portion 12 includes a pair of housingmembers 21 and 22. The housing member 21 includes a rear wall 24 and aforward wall 26, the forward wall 26 forming a sloped pulley side wallfor a supporting belt 28 and having a central hub portion 29. Thehousing member 22 includes a rear wall 30 and a forward wall 32, theforward wall 32 forming the other sloped pulley side wall for the belt28. The rear wall 30 includes an axial tubular extension 34 which ismounted on the crankshaft 14.

A spacer member 36 is mounted concentrically within the housing 22 andbetween the end walls 30 and 32. An axial opening 38 is formed throughthe spacer member 36. A passage 40 is formed longitudinally through thebody of the spacer member 36 parallel to the axial opening 38. Alongitudinal slot 42 is formed through the body of the spacer member 36diametrically opposite the longitudinal passage 40. A longitudinalopening 44 is formed through an end portion of the spacer member 36providing access between the longitudinal slot 42 and the axial opening38. A member 46 is slidably mounted in the axial opening 38 adjacent thelongitudinal opening 44. The member 46 includes an axial passage 48, acounterbored opening 50 formed in one end thereof, and an annular groove52 formed around the outer periphery and intermediate the ends thereof.An abutment or ring member 53 is secured to the member 46 on the endface opposite the counter bore 50.

A plurality of equally spaced flyweights 54 are pivotally mounted onpins 56 mounted in the body of the spacer member 36 transversely throughthe longitudinal slot 42. Each flyweight 54 is free to pivot about itsrespective pin 56 in a chamber 58 formed within the housing 22, as willbe described. A tab 60 is formed on each flyweight 54 and extendsthrough the longitudinal opening 44 into the annular groove 52 of themember 46.

A central cylindrical protrusion 62 is formed on the sloped pulley wall32 and includes an internal flange portion 64 having an axial opening 66formed therethrough. A coil spring 68 is mounted in the axial opening 38between the internal flange 64 and the end face 70 of the member 46adjacent the counter bored opening 50. A cup-shaped member 72, includingradial perforations 73, extends from the center of the sloped pulleywall 26 toward and through the axial opening 66, into the larger axialopening 38 such that the entering end thereof is surrounded by a portionof the coil spring 68. A flanged sleeve member 74 is mounted in thefully open end of the member 72 and includes a central valve seat 75.

A valve member 76 includes a head portion 78 for valving cooperationwith the seat 75 and a stem including larger and smaller diameterportions 80 and 81 with a shoulder 82 formed therebetween, the sternextending through the flanged sleeve member 74, through the length ofthe cup-shaped member 72 and an opening 83 formed in the end thereof andthence through the concentric openings 38 and 48 and the abutment orring member 53, into a counterbored opening 84 formed in the end of thecrankshaft 14. A smaller coil spring 86 is mounted concentrically withinthe larger coil spring 68 around the larger diameter stem portion 80 andbetween the intemally flanged end 88 of the cup-shaped member 72 and thebottom of the counterbore 50. Another coil spring 90 is mounted aroundthe smaller diameter extended end 81 of the valve stem, between theabutment 53 secured to the end 94 of the member 46 and a spring retainer96 formed adjacent the end of the small stem portion 81 within thecounterbore 84 of the crankshaft 14.

A fixed sloped wall member 98 is mounted within the housing 21, theslope thereof being parallel with that of the wall 26. A diaphragm 100is secured between the outer peripheral edge of the wall 98 and theinner peripheral surface of the housing member 21, providing forrelative movement between the housing member 21 and the included fixedwall 98 and forming chambers 102 and 104 on the opposing sides thereofwith the end walls 26 and 24, respectively.

A central hub portion 106 is formed on the wall 98 extending toward therear wall 24 of the housing member 21 and having an axial opening 108formed therethrough. A sleeve member 110 is secured within the axialopening 108, a seal 112 being mounted in a groove 114 formed around theinner periphery thereof. Slots 116 are formed longitudinally along theinner surface of the sleeve member 110, opening one end 1 17 to thechamber 104.

A cylindrical member 118 is slidably mounted through the sleeve member110 between the walls 24 and 26 of the housing member 21. An axialopening 120 is formed in the central member 118, and a tapered opening1.21 is formed in the member 118 to communicate between the opening 120and the slots 1 16. The axial opening 120 includes first and secondcounterbores 122 and 124, respectively, formed in one end thereof, and athird counterbore 126 formed in the other end thereof. A bearing 128 ismounted in the counterbore 124, and a spring retainer member 130 ismounted in the counterbore 126 adjacent the valve seat member 74. Afixed connector member 132 extends through the bearing 128 into thecounterbore 122, abutting against the end face of a sleeve member 133having an external flange 134 positioned in the counterbore 122 andincluding an axial passage 135. The bearing 128 is confined between aretaining ring 136 mounted in a groove 138 formed on the outer peripheryof the connector member 132 and a shoulder 140 formed thereon, andbetween a retaining member 142 mounted in a groove 144 formed on theinner surface of the central cylindrical member 1 18 and an abutment 146formed by the juncture between the counterbores 122 and 124.

A pin 148 extends from the body of the central member 1 18 into thecounterbore 122 and through an opening 150 formed in the external flange134 of the sleeve member 133, causing the latter to rotate with themember 118 against the adjacent end 152 of the connector member 132. AnO-ring seal 153 is mounted in an annular groove 154 formed around theinner surface of the central member 118 and around the outer surface ofthe sleeve member 133. A spring 156 is mounted between the springretainer member 130 and a shoulder 158 formed in the member 133. Anaxial opening 160 is formed partially through the connector member 132from the innermost end 152 thereof. A transverse opening 164 is formedthrough the connector member 132 adjacent the outermost end of the axialpassage 160, such that communication is provided between the passage 160and the opening 164. A tube or conduit 166 communicates between thetransverse passage 164 and a source of engine vacuum, representedgenerally by 168.

A plurality of stud members 170, each of which may include a smalldiameter threaded end portion 172, a two-diameter head-end portion 173and a larger two-diameter intermediate portion 174, are each mounted inaligned openings 175, 176, 177, 178, 179 and 180 formed in the rear wall30, sleeve member 36, the oppositely disposed pulley walls 32 and 26,and the hub member 106. This permits the pulley wall 26 of the housing21 to slide on the larger stem portion 174 toward and away from theadjacent pulley wall 32 of the housing 22, while causing the housing 21to rotate with the housing 22,

The upper pulley portion 16 includes axially aligned housings 181 and182. The housing 181 includes a rear wall 184 and a forward sloped wall186, the latter serving as one side of an upper pulley groove for thebelt 28. A plurality of pin members 187 are secured to an inner flatsurface portion 188 of the sloped wall 186 and each is slidably mountedin a sleeve member 189, the latter being connected for rotation with therear wall 184, thereby permitting rotation together and relative axialmovement of the walls 184 and 186 of the housing 181.

The belt 28 is mounted between the pulley wall 186 and an adjacentsloped forward wall 190 of the housing 182, the rear or left end of thehousing 182 being open. A plurality of annular V-shaped grooves 191,192, 194 and 196 are formed around the outer periphery of the housing182, suitable for having mounted therein a plurality of V-belts 198,200, 202 and 204, respectively, the latter belts being suitable fordriving engine accessories (not shown), such as a power steering pump,the air conditioner compressor and the alternator, for example.

A diaphragm 206 is mounted between the inner surface of the housing 181and a cylindrical member 208 extending from the outer edge of theforward sloped wall 186 extending toward the rear wall 184. Thediaphragm 206 serves as a means for varying the size of a chamber 210formed within the housing 181.

A pair of concentric sleeve members 212 and 214, including respectiveflanges 216 and 218, are secured to the rear wall 184 by any suitablemeans, such as bolts 220. An additional sleeve member 221 is mounted onthe member 212 adjacent the end opposite the flange 216. A gasket 222may be mounted between the flange 216 and the inner surface of the rearwall 184. A coil spring 224 is mounted radially between the outersurface of the sleeve member 212 and the inner surface of the sleevemember 214 and longitudinally between an inner surface 226 of the flange216 and a spring and seal retainer 228 mounted in a counterbored opening229 formed in the inner surface 188 of the forward sloped wall 186. Thesleeve member 212 has a large diameter opening 230 formed therein freelypositioned around a fixed cylindrical extension 232 extending from thewater pump housing 20, and a smaller diameter internal opening 234 formounting on the extended end 236 of the water pump shaft 18 and securedthereto by any suitable means, such as a setscrew 238. An O-ring seal240 is mounted between the shaft 18 and the small diameter portion 234of the sleeve member 212 in a groove 242. A pair of bearings 244 and 246are mounted between the shaft 18 and spaced inner portions of the waterpump housing extension 232. A seal member 248 is mounted around theouter periphery of the sleeve member 221 in an annular groove 250 formedin the spring and seal retainer 228. A shoulder 257 is formed on thesleeve 221 to serve as a stop for the movable pulley wall 186.

The sleeve member 212 extends into a central hub portion 252 which isformed on the inner surface of the tapered pulley wall 190, and issecured therein in any suitable manner, such as by press-fit. Aplurality of slotted passages 254 and 256 are formed on the outersurface of the sleeve member 212 adjacent the inner surface of thesleeve member 221, communicating between the chamber 210 in the housing181 and a transverse passage 258 formed adjacent the extended end 236 ofthe water pump shaft 18. A ring member 259 serves to close off the endsof the passages 254. The transverse passage 258 communicates with anaxial opening 260 formed in the extended end 236 of the shaft 18. Theopening 260 communicates with a central axial passage axial passage 262of the end portion 264 of the sleeve member 212, the end portion 264extending completely through the housing 182. Counterbores 266 and 268are formed in the extended end portion 264 of the sleeve member 212. Abearing 270, is mounted in the counterbore 268 and confined axiallytherein by a retainer ring 272 mounted in the counterbore 268 and ashoulder 274 formed by the juncture between the counterbores 266 and268. A connector member 276 is mounted through the bearing 270,extending into the counterbore 266 and having its innermost end 277abutting against a sleeve member 278. The latter is mounted in thecentral axial passage 262 of the end portion 264 and includes anexternal flange 279 positioned in the counterbore 266. Aligned axialpassages 280 and 281 are formed through the respective connector andsleeve members 276 and 278 for communication with the axial opening 260in the extended end 236 of the shaft 18.

The bearing 270 is retained axially on the connector member 276 betweena retainer ring 282 mounted in a groove 283 formed on the member 276 anda shoulder 284 formed thereon. A pin member 288 extends from the bottomof the counterbore 266 into a notch 290 formed in the flange 279 of thesleeve member 278, causing the latter to rotate with the sleeve member212 against the end 277 of the fixed connector member 276. A springretainer 292 is mounted in axial passage 262 against a shoulder 293formed in the sleeve member 212. A spring 294 is mounted between ashoulder 295 formed in the sleeve member 278 and the retainer 292. Asleeve member 298 is mounted on the outer surface of the extended endportion 264 of the sleeve member 212 and is secured thereto by anysuitable means, such as one or more bolts 300. A conventional coolingfan 302 is secured to the sleeve member 298 for rotation therewith.

A tubular conduit or passage 304 communicates between the axial opening280 of the connector member 276 of the upper pulley housing portion 182and the transverse opening 164 of the connector member 132 o the lowerpulley housing portion 21.

It may be noted that the connector member 276 of the upper pulleyassembly and the connector member 132 of the lower pulley assembly 12between which the tubular passage 304 is connected remain stationarywhile the respec tive surrounding housings 182 and 21 rotate on therespective bearings 270 and 128.

Operation We will now consider various engine operating conditions.Assume first an ENGINE-OFF/NO-VACUUM condition. Under this condition,both the lower variable chamber 104 and the upper variable chamber 210will be exposed to atmospheric pressure by virtue of there being noengine vacuum available from the vacuum source 168. Since there is nocentrifugal force at this time, the flyweights 54 would be pivoteddownwardly about the pins 56 into the longitudinal slot 42, causing thevalve head 78 to be closed tightly against the seat 75 by virtue of theforce of the spring 68 moving the member 46 to the right in FIG. 1a.

Inasmuch as the chamber 104 of the lower pulley housing 21 is exposed toatmospheric pressure, as is the adjacent chamber 102, the housing member21 will be urged to the left in FIG. la by the force of the belt 28 onthe forward sloped pulley wall 26, until the inner surface of the pulleywall 26 contacts the fixed sloped wall 98. At the same time, due to bothsides of the upper pulley wall 186 of the housing 181 being subjected toatmospheric pressure, the spring 224, whose ring end (FIG. 1) is abuttedagainst the fixed surface 226, will urge the pulley wall 186 to theleft. As a result of the above-described positions of the movable pulleywalls 26 and 186, the belt 28 will be located in the outermost portionof the upper pulley groove formed by the sloped walls 186 and 190, andin an innermost position in the lower pulley groove formed by the walls26 and 32. The respective pitch diameters at this time are substantially5% inches and 3% inches (FIG. 2).

Considering now an IDLE and/or BELOW 1,000 r.p.m. condition, the lowerchamber 104 and the upper chamber 210 will be subjected to the highestengine manifold vacuum, such vacuum having entered the chamber 104 fromthe source 168 via the passages 166, 164, 160, 120, 121, 116, and havingentered chamber 210 via the passages 166, 164, 304, 280, 281, 262, 260,258, 256 and 254. This will permit atmospheric pressure outside the rearwall 24 of the movable housing 21 to move the housing 21 to the right inFIG. 1a, causing the forward sloped pulley wall 26 to slide on thecylindrical member 118 and push the belt 28 outwardly in theprogressively narrowing groove 26/32. At the same time, atmosphericpressure on the forward sloped pulley wall 186 of the housing 181 willmove the latter to the right in FIG. 1, against the force of the spring224, and thereby expand the pulley groove 186/190' allowing theoutwardly moving lower portion of the belt 28 to pull the upper portionthereof inwardly, reaching the lower and upper diameters of 6V4inchesand 3 %inches, respectively, the resulting corresponding lower and upperpulley r.p.m.s being substantially 1,000 and 1,850, respectively, (FIG.2).

At the 1,000 r.p.m. condition, the flyweights 54 will still be at theirsubstantially innermost positions, thus maintaining the member 46 in thesame position. However, the valve seat member 74 will move to the rightin FIG. 1a along with the pulley wall 26. While this is happening, thespring 90 will urge the retainer 96 and hence the valve stem portions 80and 81 and the valve head 78 to the right, maintaining the head 78 ofthe valve 76 against the seat 75, with the shoulder 82 formed betweenthe stem portions 80 and 81 approaching the inner surface of theabutment member 53 in the axial opening 48 of the member 46.

Assume now a predetermined intermediate engine condition, such as 1,950r.p.m. The flyweights 54 will have pivoted outwardly about the pins 56under the action of centrifugal force, thus pivoting the tabs 60 in aclockwise direction, thereby sliding the member 46 to the left in FIG.la, against the force of the spring 68. The attached abutment 53 willcontact the shoulder 82 and move the stem 80, 81 and the valve head 78to the left, the latter moving away from the seat 75. This will permitair at atmospheric pressure to enter the perforations 73 in thecup-shaped member 72 and flow through the opening between the valve head78 and the seat 75 and thence through the passages 120, 121 and 116 tothe lower variable chamber 104. Additionally, the upper variable chamber210 will be subjected to a progressively decreasing engine vacuum byvirtue of the entering air being communicated thereto via the axialpassages 120, and and, thence, via the passages described above relativeto the communication of engine vacuum. This will result in the walls 24and 26 of the housing member 21 moving to the left, while the upperspring 224 moves the forward sloped pulley wall 186 of the housing 181also to the left. Hence, the upper portion of the belt 28 will be urgedoutwardly in the pulley groove 186/ 190, which movement willcorrespondingly pull the lower portion of the belt 28 radially inwardlyin the pulley groove 26/32. The resultant upper and lower pitchdiameters and speeds are substantially the same at 4 15/16 inches and1,950 r.p.m., respectively (FIG. 2).

Next, considering an ABOVE 3,000 r.p.m. condition, the flyweights 54will have continued to pivot outwardly until they have contacted theinner surface of the rear wall 30 of the housing 22. This will maintainthe valve head 78 away from the seat 75 allowing ambient air to becommunicated to the lower drive chamber 104 and the upper driven chamber210. The resultant decreased vacuum in the upper chamber 210 assists theforce of the spring 224 in moving the adjacent pulley wall 186 to theleft in FIG. 1, thereby narrowing the width of the groove 186/190. This,of course urges the upper portion of the belt 28 outwardly, pulling thelower portion of the belt 28 inwardly into the now wider groove 26/32(FIG. la), causing the lower forward movable pulley wall 26 of thehousing member 21 to move further to the left into contact with thefixed inner wall 98 and resulting in respective upper and lower pitchdiameters and speeds of substantially 5 /ainches and 1,980 r.p.m. and 3/ainches and 3,000 r.p.m., respectively (FIG. 2).

It may be noted and should now be apparent that throughout the abovecycle, the range of the upper pulley r.p.m. is relatively narrow,namely, l,850l,980, thereby rotating the fan 302 mounted on theinterconnected sleeve member 298, the water pump impeller 19 mounted onthe shaft 18, and the various engine accessories driven by the belts198, 200, 202 and 204 ata substantially constant speed, regardless ofthe varying speed of the engine.

It should also be apparent that should a hose sustain a leak or a breakat any time throughout the above cycle, the resultant influx of ambientair into the chambers 104 and 210 would cause the pulley walls 26 and286, respectively, to be moved to the left, resulting in a low ratio ofpulley 12 to pulley l0 pitch diameters, thus assuring the prevention ofany overspeeding while causing some loss in output.

While but one embodiment of the invention has been shown and described,other modifications thereof are possible.

I claim: 1

1. A drive mechanism for use with a vehicle engine for driving aplurality of engine accessories at a substantially constant speed, saiddrive mechanism comprising first, second, third,

and fourth pulley walls, a source of engine vacuum, means operativelyconnected between said source and said first and third pulley walls foraxially moving said first and third walls in opposite directions withrespect to one another in response to changes in engine vacuum,centrifugal weight means for modifying said changing engine vacuuminfluencing the movement of said first and third pulley walls withatmospheric air at ambient pressure in response to the action ofcentrifugal force reflective of engine speed, said second and fourthpulley walls being axially fixed, said first and second pulley wallsforming a first variableswidth pullcy groove and said third and fourthpulley walls forming a second variable-width pulley groove, said firstand second pulley walls being rotatable by said engine, the pitchdiameter of said first variable-width pulley groove progressivelydecreasing with increasing engine speed by virtue of said axial movementof said first wall, and the pitch diameter of said second variable-widthpulley groove progressively increasing with increasing engine speed byvirtue of said axial movement of said third wall to thereby maintain thespeed of said third and fourth pulley walls substantially constant withvarying engine speed, a cooling fan and water pump impeller speed,mounted for rotation with said third and fourth pulley walls, and aplurality of grooves formed adjacent said fourth pulley wall forrotation therewith, said grooves being suitable for having a pluralityof belts mounted therein for driving other engine accessories.

2. A drive mechanism for driving a plurality of engine accessories at asubstantially constant speed, said drive mechanism comprising a firstpulley having one axially movable wall, a second pulley having oneaxially movable wall, a source of engine vacuum, a first chamberadjacent said movable wall of said first pulley, first passage means forcommunicating the engine vacuum from said source to said first chamber,a second chamber operatively connected to said movable wall of saidsecond pulley, second passage means for communicating said engine vacuumfrom said source to said second chamber, an endless belt connectedbetween said first and second pulleys, valve means responsive tocentrifugal force for permitting air at ambient pressure to enter saidfirst and second chambers to mix with said engine vacuum therein, acooling fan mounted for rotation with said first pulley, and a pluralityof annular grooves formed on said fixed wall of said first pulley, eachof said plurality of grooves being suitable for driving a beltoperatively connected to any of said engine aceessories.

3. A drive mechanism for driving a plurality of internal combustionengine accessories at a substantially constant speed, said drivemechanism comprising a first pulley assembly having one axially movablewall portion, a second pulley assembly having one axially movable wallportion, a source of engine vacuum, a first chamber adjacent saidmovable wall of said first pulley, first passage means for communicatingthe engine vacuum from said source to said first chamber, a secondchamber operatively connected to said movable wall of said secondpulley, second passage means for communicating said engine vacuum fromsaid source to said second chamber, an endless belt mounted on saidfirst and second pulleys, said first pulley varying in width in onedirection and said second pulley varying in width in the oppositedirection in response to changes in said engine vacuum for causing saidendless belt to move radially in said pulleys to attain respective pitchdiameters as required to drive said first pulley at a substantiallyconstant speed, and means operatively connected to said first and secondchambers for modifying said engine vacuum therein with ambient pressurein response to changes in engine speed.

4. The drive mechanism described in claim 3, wherein said last-mentionedmeans includes third passage means for communicating air surroundingsaid first and second pulley assemblies to said first and secondchambers, valve means operatively connected in said third passage means,and fiyweights responsive to engine speed for varying the opening pastsaid valve means, thereby controlling the flow of ambient air therepast.

5. A drive mechanism for use with a vehicle engine for driving aplurality of engine accessories at a substantially constant speed, saiddrive mechanism comprising a first pulley assembly including first andsecond housings, said housings having adjacent walls forming a firstV-groove; a second pulley assembly rotatable by said engine andincluding third and fourth housings, said housings having adjacent wallsforming a second V-groove, portions of said first and third housingsbeing axially movable so as to vary the widths of said first and secondV-grooves; a source of engine vacuum; a first chamber adjacent saidmovable wall of said first housing; first passage means forcommunicating the engine vacuum from said source to said first chamber;spring means in said first chamber for at times urging the movable wallof said first housing toward said adjacent wall of said second chamberforming said first V-groove; a second chamber formed in said thirdhousing; second passage means for communicating said engine vacuum fromsaid source to said second chamber; an endless belt mounted in saidfirst and second V-gooves; a centrifugally actuated valve operativelyconnected to said third and fourth housings for subjecting said firstand second chambers to ambient pressure in response to engine speed; acooling fan and a water pump mounted for rotation with said first andsecond housings; and a plurality of annular grooves formed on saidsecond housing, each of said plurality of grooves being suitable fordriving a belt operatively connected to some one of said engineaccessories.

1. A drive mechanism for use with a vehicle engine for driving aplurality of engine accessories at a substantially constant speed, saiddrive mechanism comprising first, second, third and fourth pulley walls,a source of engine vacuum, means operatively connected between saidsource and said first and third pulley walls for axially moving saidfirst and third walls in opposite directions with respect to one anotherin response to changes in engine vacuum, centrifugal weight means formodifying said changing engine vacuum influencing the movement of saidfirst and third pulley walls with atmospheric air at ambient pressure inresponse to the action of centrifugal force reflective of engine speed,said second and fourth pulley walls being axially fixed, said first andsecond pulley walls forming a first variable-width pulley groove andsaid third and fourth pulley walls forming a second variable-widthpulley groove, said first and second pulley walls being rotatable bysaid engine, the pitch diameter of said first variable-width pulleygroove progressively decreasing with increasing engine speed by virtueof said axial movement of said first wall, and the pitch diameter ofsaid second variable-width pulley groove progressively increasing withincreasing engine speed by virtue of said axial movement of said thirdwall to thereby maintain the speed of said third and fourth pulley wallssubstantially constant with varying engine speed, a cooling fan andwater pump impeller speed, mounted for rotation with said third andfourth pulley walls, and a plurality of grooves formed adjacent saidfourth pulley wall for rotation therewith, said grooves being suitablefor having a plurality of belts mounted therein for driving other engineaccessories.
 2. A drive mechanism for driving a plurality of engineaccessories at a substantially constant speed, said drive mechanismcomprising a first pulley having one aXially movable wall, a secondpulley having one axially movable wall, a source of engine vacuum, afirst chamber adjacent said movable wall of said first pulley, firstpassage means for communicating the engine vacuum from said source tosaid first chamber, a second chamber operatively connected to saidmovable wall of said second pulley, second passage means forcommunicating said engine vacuum from said source to said secondchamber, an endless belt connected between said first and secondpulleys, valve means responsive to centrifugal force for permitting airat ambient pressure to enter said first and second chambers to mix withsaid engine vacuum therein, a cooling fan mounted for rotation with saidfirst pulley, and a plurality of annular grooves formed on said fixedwall of said first pulley, each of said plurality of grooves beingsuitable for driving a belt operatively connected to any of said engineaccessories.
 3. A drive mechanism for driving a plurality of internalcombustion engine accessories at a substantially constant speed, saiddrive mechanism comprising a first pulley assembly having one axiallymovable wall portion, a second pulley assembly having one axiallymovable wall portion, a source of engine vacuum, a first chamberadjacent said movable wall of said first pulley, first passage means forcommunicating the engine vacuum from said source to said first chamber,a second chamber operatively connected to said movable wall of saidsecond pulley, second passage means for communicating said engine vacuumfrom said source to said second chamber, an endless belt mounted on saidfirst and second pulleys, said first pulley varying in width in onedirection and said second pulley varying in width in the oppositedirection in response to changes in said engine vacuum for causing saidendless belt to move radially in said pulleys to attain respective pitchdiameters as required to drive said first pulley at a substantiallyconstant speed, and means operatively connected to said first and secondchambers for modifying said engine vacuum therein with ambient pressurein response to changes in engine speed.
 4. The drive mechanism describedin claim 3, wherein said last-mentioned means includes third passagemeans for communicating air surrounding said first and second pulleyassemblies to said first and second chambers, valve means operativelyconnected in said third passage means, and flyweights responsive toengine speed for varying the opening past said valve means, therebycontrolling the flow of ambient air therepast.
 5. A drive mechanism foruse with a vehicle engine for driving a plurality of engine accessoriesat a substantially constant speed, said drive mechanism comprising afirst pulley assembly including first and second housings, said housingshaving adjacent walls forming a first V-groove; a second pulley assemblyrotatable by said engine and including third and fourth housings, saidhousings having adjacent walls forming a second V-groove, portions ofsaid first and third housings being axially movable so as to vary thewidths of said first and second V-grooves; a source of engine vacuum; afirst chamber adjacent said movable wall of said first housing; firstpassage means for communicating the engine vacuum from said source tosaid first chamber; spring means in said first chamber for at timesurging the movable wall of said first housing toward said adjacent wallof said second chamber forming said first V-groove; a second chamberformed in said third housing; second passage means for communicatingsaid engine vacuum from said source to said second chamber; an endlessbelt mounted in said first and second V-gooves; a centrifugally actuatedvalve operatively connected to said third and fourth housings forsubjecting said first and second chambers to ambient pressure inresponse to engine speed; a cooling fan and a water pump mounted forrotation with said first and second housings; and a plurality of annulargrooves formed on said second housing, each of said plurality of groovesbeing suitable for driving a belt operatively connected to some one ofsaid engine accessories.